Benzene, Chapter 25 Flashcards
What is the formula for benzene?
C6H6
Describe Benzene?
- colourless, sweet smelling and highly flammable.
- found naturally in crude oil and petrol.
- classified as a carcinogen, that can cause cancer.
What is the derivative of benzene?
It is aromatics.
How reactive is benzene?
It is not very reactive, as
Benzene does not undergo electrophilic addition reactions
Benzene does not decolourise bromine under normal conditions.
Describe the delocalised model of benzene.
It is a planar, cyclic, hexagonal hydrocarbon containing six carbon atom and six hydrogen atoms.
Each carbon atom uses three of its available four electrons in bonding to two other carbon atoms and to one hydrogen atom.
Each carbon atom has 1 electron in a p-orbital at right angles to the plane of the bonded carbon and hydrogen atoms, the overlapping p-orbitals creates a system of pi bonds which spread over all six of the carbon atoms in the ring structure.
The 6 electrons occupying this system of pi-bonds are said to be delocalised.
Naming aromatic compounds.
Nitration of benzene
Benzene reacts slowly with nitric acid to form nitrobenzene.
The reaction is catalysed by sulphuric acid and heated to 50c to obtain a good rate of reaction, and water bath is used to maintain the steady temperature.
One of the hydrogen atoms on. The benzene ring is replaced by a nitro [-NO2].
Halogenation of benzene
Halogens DO NOT react with benzene unless there is a catalyst called a halogen carrier is present. It occurs at room temperature.
Alkylation reactions
It increases the number of Caron atoms in a compound by forming carbon-carbon bonds.
This is called Friedel-Crafts alkylation after the two chemists first carried out the reaction.
In the presence of AlCl3.
Acylation reactions
Benzene reacts with an acrylic chloride in the presence of an AlCl3 catalyst, and an aromatic ketone is formed, it is another example of electrophilic substitution.
Why doesn’t benzene not decolourise bromine?
This is because benzene has delocalised electrons that are spread above and below the plane of the carbon atoms.
The electron density around any two of the carbon atoms in the ring is less the c=c bond in a alkene. It has a low electron density.
What is the difference between phenyl and benzene?
The difference is that benzene contains 6 hydrogen atoms whereas, phenyl is derivative of benzene which contain 5 hydrogen atoms.
Describe phenols.
Type of organic compound contains an -OH group directly binds to an aromatic ring.
The simplest on is C6H5OH.
Why is phenol classified as weak acid?
When dissolved in water phenol partially dissociates forming the phenoxide ion and a proton, because of this ability to produce proton when partially dissociating it is classified as weak acid.
How can nitrobenzene react with bromine
It reacts slowly with halogen and will so need a catalyst and a high temperature.
